Easy fix for AC Motor Starter Chatter? 2

[Logicon]

I have read several of the historical threads related to AC motor starter chatter. I have a similar issue with an 80HP 480 VAC motor controlled by an IEC starter with a 120VAC coil. System is powered from a 208 service stepped up to 480VAC. The 120 control voltage (300VA) dips to around 100-105vac (with fluke meter not scope) while attempting to pull it in. The coil is rated for 95-180vac. Sometimes it does pull in, but mostly it doesn't and chatters something fierce. I have seen comments on changing to a DC coil starter and using rectifiers. I am looking for the right solution or other ideas. As a PLC guy I am mostly use to just firing the output.

Sorry to bring up a recurring topic.


Marc Whitney

http://www.thelogicongroup.com

 

[dpc]

I have ordered a constant voltage power conditioner with high hopes

I would use a true UPS with an inverter fed from a battery that is floating on a charger.

Not sure a power conditioner is going to keep the voltage up well enough when the source voltage tanks.

David Castor

http://www.cvoes.com

 

[Laplacian]

I don't know why you guys are so strong on the UPS recommendation. They require battery replacement or complete replacement every few years. In an industrial environment where preventive maintenance is always "tested", the UPS will likely run to failure resulting in more contactor chatter when the battery fails. The CVT will be there for 20+ years without giving it a second thought. They have suprising voltage hold up capability depending on loading. Even at full load, 80% input voltage provides 100% output continuously.

Their disadvantage besides generating heat and being extremely inefficient is they have no fault current capability. Max output current is basically the rated load output so it will not clear protective devices.

 

[dpc]

Laplacian,

If it can support the voltage, it's probably a good solution. I don't have any confidence that we actually know what the voltage is dipping to.

I don't actually like the UPS solution for a lot of reasons, but it will definitely work, as the OP has already proved. The CVT may or may not work. Seems like an expensive experiment.

The real solution is to get a bigger source or put in a reduced voltage starter or VFD.

 

[jraef]

In my opinion the UPS solution is like trweating pneumonia with cough syrup. It may take care of a symptom but it's not taking care of the problem.

FWIW.

 

[itsmoked]

My recommendation for a UPS is only to prove/disprove a screwed up contactor. Not a permanent solution.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Regarding the UPS - Sometimes, you have to work with what you have even if that not the preferred solution.

I personally don't feel a CVT is such an easy solution either. Capacitors often fail well inside 20 years.

 

[OperaHouse]

Here is another idea. Use a quite high boost transformer (maybe double the voltage) with a resistor in series with the relay. The resistor is selected to supply nominal voltage to the MCR when things are back to normal. An ON DELAY relay is powered in parallel with the MCR. The relays NC contacts short out the resistor for a boost and then open after motor is up to speed. On delay must be a relay type and universal voltage type capable at the higher voltage. Creates a little heat but uses all standard components.

I worked on a friends Miller welder years and they used (I think)a lower voltage MCR with a resistor in series to handle line drop. Thought it interesting at the time.

 

[Logicon]

****************** RESOLUTION *******************

SUCCESS - with a 500VA power conditioner. Wired 120vac from exisitng 300VA control XFMR through new power conditioner from Sola and fed 120vac for the system. Works like a champ. Special thanks to Laplacian for the early suggestion.

I was not on site to monitor or inspect the resulting voltages but my electrician called to indicate 100% success and no sign of chatter in the starter.

Thanks to all for the information. I have learned a lot!


Marc Whitney

http://www.thelogicongroup.com

 

[waross]

Thank you for the update, Logicon.

Bill
--------------------
"Why not the best?"
Jimmy Carter